12/1/2008 | 9 MINUTE READ

Diesel's Challenge: Acceptance in America

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The Europeans are coming with diesels. They make sense in Europe. But what about the U.S.? We look at the numbers. And drive an Audi more than 1,800 miles to find out.


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In 1993, oil consumption in Germany, Europe's largest auto market, was 2.89 million barrels/day. In the U.K., they were consuming 1.83 million barrels/day. In the U.S., 16.8 million barrels per day were being used in 1993. Fast forward to 2007, when there were more vehicles on the road in all three countries, and more miles driven. The amount of oil used in Germany fell to 2.44 million barrels per day. The U.K. cut its demand to 1.66 million barrels/day. Meanwhile, in the U.S. demand rose to 20.68 million barrels in 2007.

What was the difference in demand? Arguably, diesel. Beginning in the late 1990s, European manufacturers and governments worked together to develop policies that would help reduce the continent's reliance on foreign oil, while improving fuel efficiency, and cutting CO2 emissions. The scheme called for focused taxation and regulation that encouraged manufacturers and consumers to embrace diesel-powered vehicles for their extended range-upwards of 30% in some cases-without sacrificing low-end torque-the pulling power most U.S. consumers confuse with horsepower.

So why hasn't diesel gained traction in the U.S.? There are a number of factors playing against diesel: a higher per-gallon price, more expensive engines (some experts claim a $2,500 premium), tight particulate and NOx emission regulations that require expensive aftertreatment, and a negative image. Not only are they seen as being dirty, loud and smelly, in the U.S. diesels have an image for roughness and unreliability that dates back to GM's miserable LF9 and LF7 engines of the 1980s. More important than this, however, is the fact that European countries adopted a tax rebate system that encourages diesel ownership. That's a major reason why they account for 53% of new light-vehicle sales in Western Europe. And it is doubtful that without a change in tax policy they will span the 48% gap between their current U.S. light-vehicle penetration rates and Europe's. Yet these obstacles aren't stopping European automakers from exporting diesel technology to the U.S. Mercedes, BMW, and VW have entries in the U.S. market, and Audi's 3.0-liter V6 TDI engine-found under the hood of the 2009 Q7 SUV-follows in early 2009.

Audi's Ode to Rudolf Diesel
Audi claims the 3.0-liter is "the world's cleanest diesel engine" thanks to the addition of an advanced low-emissions system designed to meet the EPA's aggressive Tier II BIN 5 regulations. The system utilizes an oxidation catalyst, particulate filter, and a urea metering unit upstream of the DeNOx converter. Exhaust heat breaks the 32.5% urea solution down into ammonia which splits the nitrous oxide into nitrogen and hydrogen and reduces NOx emissions by as much as 90%. The engine features four valves per cylinder, 90o bank angle with 90 mm between bore centers and a vermicular graphite cast iron block (Audi claims this material is 15% lighter than cast iron-resulting in an overall dressed weight of just 498.2 lb.). The camshafts and ancillaries are driven from the back of the engine to reduce engine height at the front. This makes it easier for Audi to meet European pedestrian crash standards.

Fuel delivery is managed by the third generation common rail system developed by Robert Bosch LLC, and utilizes variable piezo injector technology with a pressure output of 1,800 bar. Power and efficiency are aided by variable turbo technology from Honeywell Garrett that produces boost pressure across a wide range of engine speeds. These systems combine to produce a power output rating of 225 hp @ 4,000 to 4,500 rpm and maximum torque output of 550 lb.-ft. @ 2,000 to 2,500 rpm. Audi claims the diesel Q7-curb weight 6,500 lb.-is EPA rated at 17 mpg city/24 mpg highway versus 14 city/20 highway for the gasoline-powered V6 model. Undoubtedly, much of that difference is due not only to the greater energy per unit diesel can produce versus gasoline, but also the puny, by comparison, 266 lb.-ft. of torque @ 2,750 rpm of the gasoline engine.

Living with Diesel

I spent four days and traveled 1,800 miles in a diesel-powered ’09 Audi Q7, during which time I learned that today’s diesels are clean, quiet, and—a blast to drive. It was part of Audi’s coast-to-coast Mileage Marathon, a competition with one simple goal: achieve the best mpg and the highest mph over the course of the event. The competition was sanctioned by the International Motor Sports Association. Computers were tucked in the rear tire well to keep track of fuel flow and other statistics. A holographic seal was affixed on the fuel filler doors at each fill up and signed by the officials to prevent any cheating.


Day one: Chicago to Memphis
“What’s the problem?” we were asked by an Illinois state trooper as we sat on the side of the road. We were trying to get to Memphis. The navigation system wasn’t helping. The first checkpoint was Salem, IL. The state trooper didn’t know where it is, either. He went to his squad car to ask the dispatcher where it is. We managed to get the navigation system to route us there. We arrived in Salem with 50 additional miles on our odo than the rest of the group thanks to the navigation error. Along the route, I took note of fuel prices (this was in early October) and was startled to discover that it cost an extra $0.48 per gallon to purchase diesel fuel in Illinois when compared to regular unleaded ($3.99/gal. vs. $3.47/gal). Once we crossed into Missouri the situation worsened to $0.73/gal. ($3.72/gal. vs. $2.99/gal.). At the end of the afternoon, it was time to take in some barbeque at the famed B.B. King’s on Main Street in Memphis. We ended the day in third place.


Day two: Memphis to Dallas
The day started off with a quick detour to the famed Elvis statue in downtown Memphis, where we snapped a souvenir photo of the Q7 parked at the foot of The King. Once out of downtown Memphis, we headed west along Interstate 40 for the longest part of our journey. We were serious about winning the competition, so we deployed what we thought were the ideal tactics to victory: Use the manual shifting function on the gearbox to keep the transmission in the highest gear possible at all times; take advantage of the Q7’s adjustable suspension—the “dynamic” mode automatically lowers the ride height 15 mm at higher speeds—to help reduce wind resistance, thus improving overall fuel economy. We set the cruise control at about 72 mph and maintained between 2,000 and 2,500 rpm, which turned out to be the sweet spot for the Q7. Finally, the biggest benefit to improved miles per gallon turned out to be drafting behind a semi-truck: it was quite obviously late for a delivery as it was traveling at an average speed of approximately 70 mph for the more than 120 miles we tagged along, helping us add 2 mpg onto our fuel economy average. While the trucker didn’t take us all the way into Dallas, once he pulled off the road he gave us a honk of his horn and we returned the gesture with a big thumbs up—it’s good to have friends in the trucking community, even though we were in an SUV, not a big rig. During this part of our adventure, the price premium for diesel over regular unleaded fluctuated wildly. In Arkansas, diesel was $0.46/gal more expensive ($3.65/gal. vs. $3.19), while in Texas the price gap grew to $0.86/gal. ($3.75/gal. vs. $2.89/gal.). Our relentless attention to detail—and the rolling brick that cut the wind for us—put us in first place for the day.

Day three: Dallas to Amarillo
Our intent was clear: pay the same meticulous attention to detail as we did the day before. We traveled west along I-20, across some back country roads and onto I-40 west to Amarillo. During dinner the previous night, we stupidly let our key secret out of the bag to another team, telling them of our helpful trucker. As one might expect, they found themselves a very fast semi and tucked behind; we gave them unpleasant gestures to signify our unhappiness as they passed by. Eventually we found our own semi traveling about 70 mph and again we followed the practice that paid off the day before—if it ain’t broke, don’t fix it, right? Once we got to the gas station to refill our vehicle at the end of the route—diesel lovers need to avoid Amarillo like the plague since it had the highest disparity when it came to the per gallon cost of diesel vs. regular gasoline at $0.92/gal. ($3.64/gal. vs. $2.72/gal)—our “tactic stealers” were waiting to rub their fuel consumption numbers in our face when, until the IMSA officials told us our Q7 required less fuel at fill-up than theirs. “What in the [expletive] are you guys doing?” the envious competitor asked. We just smiled and moved along to enjoy the evening rodeo. Yet again, we ended up with the gold for the day.

Day four: Amarillo to Denver
Altitude can be a very bad thing for fuel economy. Add to that an expected wind storm and heavy rain, and you know it’s going to be an ugly day. Our decision: Hit the high-speed goal while driving on U.S. 27 through the (relatively) flat lands of Texas and then worry about fuel economy once we hit the higher elevations. It was pedal to the metal for the first 50 to 75 miles. Then, once we ended up crossing the New Mexico border, it was time to get serious. We kept the Q7 in 6th gear and took our foot off the accelerator on downhill maneuvers, watching our instantaneous fuel economy numbers climb. Speeds were kept at a more pedestrian rate of between 60 and 65 mph, a pace we thought would give us the edge. Once through Pueblo, we realized it was time to find someone who could cut the wind for us. We tucked behind a few RVs and then found a truck to clip onto for a few miles, but most of the drive was solo and we watched our average economy drop bit by bit as we climbed into the Mile High City where the diesel price gap was the second largest on record—$0.90/gal—($3.75/gal. vs. $2.85/gal.).

Once the day ended, an IMSA official delivered the overall results for the four days of our journey. We won the gold by achieving an average speed of 61.6 mph and average consumption of 29.6 mpg after covering 1,842 miles of concrete in a Q7 weighing more than 6,500 lb. with loads of luggage and other gear.

So, am I convinced about the benefit of diesel? Diesel prices were an average 23% higher than regular unleaded over the four days, resulting in an added burden placed on top of the already difficult price premium added for opting for a diesel engine in the first place—as much as $2,500. This virtually eliminates the economic benefits of diesel. However, even right-brain thinkers may marvel at the enormous low-end power and fun-to-drive exhilaration diesel power provides, and forget about those pesky complicated mathematical equations. 

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